1. Field of the Invention
The present invention relates to systems and methods of tracking remote stations, and in particular to a method and system for tracking a remote station.
2. Description of the Related Art
The tracking of enterprise assets is a common problem for many businesses. Such enterprise assets include for example, stationary assets such as product inventory, business files and computers, and mobile assets such as fork lifts, test equipment, etc. The problems encountered in keeping track of enterprise assets increase dramatically as the number of assets increase.
Optical bar code devices offer one solution to the asset-tracking problem. With these systems, a bar code is placed on a visible surface of the asset. When a user moves the asset, a bar code reader is used to xe2x80x9ccheck outxe2x80x9d the asset, and indicate that possession (and presumably responsibility for the asset) has been reassigned from its present custodian (which may be file room, equipment room, or inventory storage facility) to a new custodian. Thereafter, the new custodian can transfer possession and responsibility to yet another custodian by again scanning the barcode on the asset with another bar code reader. Using this method, the custodian of the package can be determined at any arbitrary time, and the location of the package can be thus determined. The problem with such systems is that many users fail to scan the barcode before taking possession for the asset. When this occurs, the custodian (and hence, the location) of the asset will be unknown to the system.
Other devices for determining the location of an asset are known in the art. For example U.S. Pat. No. 5,218,344 teaches determination of the position of an asset from the time of arrival of a radio frequency (RF) signal. Unfortunately, this solution is unsuitable for low-value assets disposed over relatively short distances. Because the propagation speed of the RF signal is the speed of light (about 30 centimeters per nanosecond), high precision electronics are required to determine ranging over short (20 meters or so) distances.
Similarly, U.S. Pat. No. 5,621,338 teaches the detection of pre-selected distances using an in-range/out-of-range determination. While useful to bound a tracked object within certain boundaries, it does not provide an indication of the precise location of the asset.
U.S. Pat. No. 5,021,794 teaches the use of an ultra high frequency (UHF) radio direction finding and distance measurement which uses the RF signal strength for ranging. However, radio waves in the UHF band can be widely scattered by common environmental materials, resulting in unreliable ranging estimates over short distances.
As can be seen from the foregoing, there is a need for a system for tracking assets that does not rely on any overt actions on the part of current or potential custodians, and yet provide a low cost, high accuracy tracking of the asset at relatively short distances. The present invention satisfies that need.
To address the requirements described above, the present invention discloses a method and apparatus for tracking assets from a base station.
The method comprises the steps of generating a magnetic field at the base station, receiving a radio signal transmitted from the remote station disposed at a location, and determining a distance from the base station to the location from the received radio signal transmitted from the remote station. In another embodiment of the invention, the method comprises the steps of remotely sensing a magnetic field generated by a base station, measuring an intensity of the sensed magnetic field, and transmitting a radio signal from the remote station to the base station as an indication of a distance between the base station and the remote station.
The apparatus comprises a magnetic field generator, a receiver for receiving a signal from a remote station indicative of a distance between the base station and the remote station, and a processor, coupled to the magnetic field generator and the receiver, the processor for determining a distance from the remote location to the base station from the received signal. In one embodiment, the processor is embodied in discrete components that generate a signal proportional to the distance between the remote location and the base station. In another embodiment, the processor includes a digital processing unit communicatively coupled to a memory having instructions for computing the distance between the remote location and the base station from the received signal.
The present invention achieves the goal of asset location and management without requiring an active intervention by the custodian or expensive electronics. In one embodiment, the base station emits an undulating magnetic field. A remote station is placed on or near the asset to be tracked. In one embodiment, the remote station is embodied in a card having a magnetic field sensor that transmits a radio frequency identification (RF) signal when the measured magnetic field exceeds a detection threshold. Since the detection threshold and field strength of the magnetic field at the base station is known or can be determined, the distance between the base station and the card is computed from the time that the RF signal is received from the card. The RF signal identifies the card to the base station at the time of field detection and hence the distance is proportional to the square root of the magnetic field strength at the time of detection.